Analytica Chimica Acta (v.881, #C)

Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: A review by Madalina M. Barsan; M. Emilia Ghica; Christopher M.A. Brett (1-23).
Display OmittedThe aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.
Keywords: Redox polymers; Conducting polymers; Phenazines; Triphenylmethanes; Carbon nanotubes; Electrochemical (bio) sensors;

Combining multiset resolution and segmentation for hyperspectral image analysis of biological tissues by S. Piqueras; C. Krafft; C. Beleites; K. Egodage; F. von Eggeling; O. Guntinas-Lichius; J. Popp; R. Tauler; A. de Juan (24-36).
Display OmittedHyperspectral images can provide useful biochemical information about tissue samples. Often, Fourier transform infrared (FTIR) images have been used to distinguish different tissue elements and changes caused by pathological causes. The spectral variation between tissue types and pathological states is very small and multivariate analysis methods are required to describe adequately these subtle changes.In this work, a strategy combining multivariate curve resolution-alternating least squares (MCR-ALS), a resolution (unmixing) method, which recovers distribution maps and pure spectra of image constituents, and K-means clustering, a segmentation method, which identifies groups of similar pixels in an image, is used to provide efficient information on tissue samples. First, multiset MCR-ALS analysis is performed on the set of images related to a particular pathology status to provide basic spectral signatures and distribution maps of the biological contributions needed to describe the tissues. Later on, multiset segmentation analysis is applied to the obtained MCR scores (concentration profiles), used as compressed initial information for segmentation purposes. The multiset idea is transferred to perform image segmentation of different tissue samples. Doing so, a difference can be made between clusters associated with relevant biological parts common to all images, linked to general trends of the type of samples analyzed, and sample-specific clusters, that reflect the natural biological sample-to-sample variability. The last step consists of performing separate multiset MCR-ALS analyses on the pixels of each of the relevant segmentation clusters for the pathology studied to obtain a finer description of the related tissue parts. The potential of the strategy combining multiset resolution on complete images, multiset segmentation and multiset local resolution analysis will be shown on a study focused on FTIR images of tissue sections recorded on inflamed and non-inflamed palatine tonsils.
Keywords: FTIR macroscopic imaging; Multiset analysis; Image resolution; Unmixing; Local MCR-ALS; Image multiset segmentation; Tonsil inflammation disease;

Sensitive determination of 17β-estradiol in river water using a graphene based electrochemical sensor by Fernando C. Moraes; Bruno Rossi; Maria C. Donatoni; Kleber T. de Oliveira; Ernesto C. Pereira (37-43).
Display OmittedIn this study, a novel material for the electrochemical determination of 17β-estradiol using an electrode based on reduced graphene oxide and a metal complex porphyrin has been applied to environmental monitoring. The electrochemical profile of the proposed electrode was analyzed by differential pulse voltammetry, which showed a shift of the oxidation peak potential of 17β-estradiol to 150 mV in a less positive direction compared to the bare reduced graphene oxide electrode. DPV experiments were performed in PBS at pH 7.0 to determine 17β-estradiol without any previous step of extraction, cleanup, or derivatization, in the range of 0.1–1.0 μmol L−1 with a detection limit archived at 5.3 nmol L−1 (1.4 μg L−1). The proposed sensor was successfully applied in the determination of 17β-estradiol in a river water sample without any purification step and was successfully analyzed under the standard addition method. All the obtained results were in agreement with those from the HPLC procedure.
Keywords: Reduced graphene oxide; Metallic porphyrin; 17β-estradiol; River water;

Display OmittedThe paper presents the first report on fabrication and application of a user friendly and mercury free electrochemical sensor, with the renewable bismuth bulk annular band working electrode (RBiABE), in stripping voltammetry (SV). The sensor body is partly filled with the internal electrolyte solution, in which the RBiABE is cleaned and activated before each measurement. Time of the RBiABE contact with the sample solution is precisely controlled. The usefulness of this sensor was tested by Ni(II) and Co(II) traces determination by means of differential pulse adsorptive stripping voltammetry (DP AdSV), after complexation with dimethylglyoxime (DMG) in ammonia buffer (pH 8.2). The experimental variables (composition of the supporting electrolyte, pre-concentration potential and time, potential of the RBiABE activation, and DP parameters), as well as possible interferences, were investigated. The linear calibration graphs for Ni(II) and Co(II), determined individually and together, in the range from 1 × 10−8 to 70 × 10−8  mol L−1 and from 1 × 10−9 to 70 × 10−9  mol L−1 respectively, were obtained. The calculated limit of detection (LOD), for 30 s of the accumulation time, was 3 × 10−9  mol L−1 for Ni(II) in case of a single element’s analysis, whereas the LOD was 5 × 10−9  mol L−1 for Ni(II) and 3 × 10−10  mol L−1 for Co(II), when both metal ions were measured together. The repeatability of the Ni(II) and Co(II) adsorptive stripping voltammetric signals obtained at the RBiABE were equal to 5.4% and 2.5%, respectively (n  = 5). Finally, the proposed method was validated by determining Ni(II) and Co(II) in the certified reference waters (SPS-SW1 and SPS-SW2) with satisfactory results.
Keywords: Bismuth bulk electrode; Stripping voltammetry; Nickel; Cobalt; Water analysis; Mercury-free electroanalysis;

Display OmittedA simple dispersive solid-phase micro-extraction method based on CoFe2O4 nano-particles (NPs) functionalized with 8-hydroxyquinoline (8-HQ) with the aid of sodium dodecyl sulfate (SDS) was developed for separation of Al(III) ions from aqueous solutions. Al(III) ions are separated at pH 7 via complex formation with 8-HQ using the functionalized CoFe2O4 nano-particles sol solution as a dispersed solid-phase extractor. The separated analyte is directly quantified by a spectrofluorometric method at 370 nm excitation and 506 nm emission wavelengths. A comparison of the fluorescence of Al(III)–8-HQ complex in bulk solution and that of Al(III) ion interacted with 8-HQ/SDS/CoFe2O4 NPs revealed a nearly 5-fold improvement in intensity. The experimental factors influencing the separation and in situ monitoring of the analyte were optimized. Under these conditions, the calibration graph was linear in the range of 0.1–300 ng mL−1 with a correlation coefficient of 0.9986. The limit of detection and limit of quantification were 0.03 ng mL−1 and 0.10 ng mL−1, respectively. The inter-day and intra-day relative standard deviations for six replicate determinations of 150 ng mL−1 Al(III) ion were 2.8% and 1.7%, respectively. The method was successfully applied to direct determine Al(III) ion in various human serum and water samples.
Keywords: Al(III) ion; CoFe2O4 nano-particles; 8-Hydroxyquinoline; Direct determination; Spectrofluorometry;

Display OmittedVolumetric absorptive microsampling (VAMS) is a novel sampling technique that allows the straightforward collection of an accurate volume of blood (approximately 10 μL) from a drop or pool of blood by dipping an absorbent polymeric tip into it. The resulting blood microsample is dried and analyzed as a whole. The aim of this study was to evaluate the potential of VAMS to overcome the hematocrit bias, an important issue in the analysis of dried blood microsamples. An LC-MS/MS method for analysis of the model compounds caffeine and paraxanthine in VAMS samples was fully validated and fulfilled all pre-established criteria. In conjunction with previously validated procedures for dried blood spots (DBS) and blood, this allowed us to set up a meticulous comparative study in which both compounds were determined in over 80 corresponding VAMS, DBS and liquid whole blood samples. These originated from authentic human patient samples, covering a wide hematocrit range (0.21–0.50). By calculating the differences with reference whole blood concentrations, we found that analyte concentrations in VAMS samples were not affected by a bias that changed over the evaluated hematocrit range, in contrast to DBS results. However, VAMS concentrations tend to overestimate whole blood concentrations, as a consistent positive bias was observed. A different behavior of VAMS samples prepared from incurred and spiked blood, combined with a somewhat reduced recovery of caffeine and paraxanthine from VAMS tips at high hematocrit values, an effect that was not observed for DBS using a very similar extraction procedure, was found to be at the basis of the observed VAMS-whole blood deviations. Based on this study, being the first in which the validity and robustness of VAMS is evaluated by analyzing incurred human samples, it can be concluded that VAMS effectively assists in eliminating the effect of hematocrit.
Keywords: Dried blood spots; Volumetric absorptive microsampling; Hematocrit; Caffeine; Paraxanthine; Liquid chromatography–tandem mass spectrometry;

Display OmittedSoxhlet extraction is a popular sample preparation technique used in chemical analysis. It enables liberation of molecules embedded in complex matrices (for example, plant tissues, foodstuffs). In most protocols, samples are analyzed after the extraction process is complete. However, in order to optimize extraction conditions and enable comparisons between different types of extraction, it would be desirable to monitor it in real time. The main development of this work is the design and construction of the interface between Soxhlet extractor and GC–MS as well as ESI-MS system. The temporal extract profiles, obtained in the course of real-time GC–MS monitoring, have been fitted with mathematical functions to analyze extraction kinetics of different analytes. For example, the mass transfer coefficients of pinene, limonene and terpinene in lemon sample, estimated using the first-order kinetic model, are 0.540 h−1, 0.507 h−1 and 0.722 h−1, respectively. On the other hand, the Peleg model provides the following extraction rates of pinene, limonene and terpinene: 0.370 nM h−1, 0.216 nM h−1 and 0.596 nM h−1, respectively. The results suggest that both first-order kinetic and Peleg equations can be used to describe the progress of Soxhlet extraction. On-line monitoring of Soxhlet extraction reveals extractability of various analytes present in natural samples (plant tissue), and can potentially facilitate optimization of the extraction process.
Keywords: Extraction kinetics; Hyphenation; On-line methods; Sample preparation; Time-resolved extraction;

A bare-eye based one-step signal amplified semiquantitative immunochromatographic assay for the detection of imidacloprid in Chinese cabbage samples by Qingkui Fang; Limin Wang; Qi Cheng; Jia Cai; Yulong Wang; Mingming Yang; Xiude Hua; Fengquan Liu (82-89).
Display OmittedA novel bare-eye based one-step signal amplified semi-quantitative immunochromatographic assay (SAS-ICA) was developed for detection of the pesticide imidacloprid. This method was based on competitive immunoreactions. Signal amplification was achieved by dual labeling of the test lines (TLs) on the strip using high affinity nanogold-biotinylated anti-imidacloprid mAb (BAb) and nanogold-streptavidin (Sa) probes. The relative color intensities of three TLs (TL-I, TL-II and TL-III) on a nitrocellulose (NC) membrane were used for direct visual analysis of the SAS-ICA strips, and could be used for semi-quantitation of analyte concentrations by observing what TLs disappeared in the amplification zone. Under optimized conditions, the following imidacloprid concentration ranges would be detected by visual examination of the SAS-ICA strip: 0–5 ng mL−1 (negative samples), and 5–25 ng mL−1, 25–250 ng mL−1, 250–1000 ng mL−1 and >1000 ng mL−1 (positive samples). The sensitivity (the visual detection limit (VDL) of TL-III) and semi-quantitative analytical capacity (when TL-III disappeared completely) of the SAS-ICA strip were 10-fold and 160-fold higher than those of traditional ICA, respectively. The developed SAS-ICA strip was applied to the analysis of spiked and authentic contaminated Chinese cabbage samples in the laboratory and under field conditions, and the results were validated by high-performance liquid chromatography (HPLC). This process could be adopted as a potential generous technique for all ICA-based detection methods.
Keywords: Signal amplification; Bare-eye based semi-quantitative; Immunochromatographic assay; Imidacloprid; Chinese cabbage;

Dispersion in cylindrical channels on the laminar flow at low Fourier numbers by Witold Kucza; Juliusz Dąbrowa; Katarzyna Nawara (90-97).
Display OmittedA numerical solution of the uniform dispersion model in cylindrical channels at low Fourier numbers is presented. The presented setup allowed to eliminate experimental non-idealities interfering the laminar flow. Double-humped responses measured in a flow injection system with impedance detection agreed with those predicted by theory. Simulated concentration profiles as well as flow injection analysis (FIA) responses show the predictive and descriptive power of the numerical approach. A strong dependence of peak shapes on Fourier numbers, at its low values, makes the approach suitable for determination of diffusion coefficients. In the work, the uniform dispersion model coupled with the Levenberg–Marquardt method of optimization allowed to determine the salt diffusion coefficient for KCl, NaCl, KMnO4 and CuSO4 in water. The determined values (1.83, 1.53, 1.57 and 0.90) × 10−9  m2  s−1, respectively, agree well with the literature data.
Keywords: Flow injection system; Impedance measurements; Numerical modeling; Optimization; Diffusion coefficient;

Display OmittedAn alternative analysis technique for the quantitation of 15 poly- and perfluoroalkyl substances (PFASs) in water matrices is reported. Analysis time between each sample was reduced to less than 20 s, all target molecules being analyzed in a single run with the use of laser diode thermal desorption atmospheric pressure chemical ionization (LDTD/APCI) coupled with high resolution accurate mass (HRMS) orbitrap mass spectrometry. LDTD optimal settings were investigated using either one-factor-at-a-time or experimental design methodologies, while orbitrap parameters were optimized simultaneously by means of a Box–Behnken design. Following selection of an adequate sample concentration and purification procedure based on solid-phase extraction and graphite clean-up, the method was validated in an influent wastewater matrix. Environmentally significant limits of detection were reported (0.3–4 ng L−1 in wastewater and 0.03–0.2 ng L−1 in surface water) and out of the 15 target analytes, 11 showed excellent accuracies (±20% of the target values) and recovery rates (75–125%). The method was successfully applied to a selection of environmental samples, including wastewater samples in 7 locations across Canada, as well as surface and tap water samples from the Montreal region, providing insights into the degree of PFAS contamination in this area.
Keywords: Perfluorinated; Wastewater; Laser diode thermal desorption; High resolution accurate mass; Orbitrap; Experimental design;

Display OmittedMetabolomic profiling involves relative quantification of metabolites in comparative samples and identification of the significant metabolites that differentiate different groups (e.g., diseased vs. controls). Chemical isotope labeling (CIL) liquid chromatography–mass spectrometry (LC–MS) is an enabling technique that can provide improved metabolome coverage and metabolite quantification. However, chemical identification of labeled metabolites can still be a challenge. In this work, a new set of isotopic labeling reagents offering versatile properties to enhance both detection and identification are described. They were prepared by a glycine molecule (or its isotopic counterpart) and an aromatic acid with varying structures through a simple three-step synthesis route. In addition to relatively low costs of synthesizing the reagents, this reaction route allows adjusting reagent property in accordance with the desired application objective. To date, two isotopic reagents, 4-dimethylaminobenzoylamido acetic acid N-hydroxylsuccinimide ester (DBAA-NHS) and 4-methoxybenzoylamido acetic acid N-hydroxylsuccinimide ester (MBAA-NHS), for labeling the amine-containing metabolites (i.e., amine submetabolome) have been synthesized. The labeling conditions and the related LC–MS method have been optimized. We demonstrate that DBAA labeling can increase the metabolite detectability because of the presence of an electrospray ionization (ESI)-active dimethylaminobenzoyl group. On the other hand, MBAA labeled metabolites can be fragmented in MS/MS and pseudo MS3 experiments to provide structural information on metabolites of interest. Thus, these reagents can be tailored to quantitative profiling of the amine submetabolome as well as metabolite identification in metabolomics applications.
Keywords: Mass spectrometry; Liquid chromatography; Isotope labeling; Amine-containing metabolites; Metabolomics;

Display OmittedIn the present study, an inductively-coupled plasma-mass spectrometry (ICP-MS)-based triple-amplification system, by combination of nicking–displacement, rolling circle amplification (RCA) and bio-bar-code probes, was fabricated for the detection of DNA target. By using this system, hepatitis B virus (HBV) DNA target down to 3.2 × 10−17  M was detected by DNA probes labeled with Au nanoparticles (AuNPs). Single nucleotide polymorphisms in genes can also be effectively discriminated. In addition, we proved that this strategy is capable of detecting the target in complicated biological samples and holds great potential application in biomedical research.
Keywords: Inductively-coupled plasma-mass spectrometry; Rolling circle amplification; Bio-bar-code; Triple-amplification; Hepatitis B virus;

Strand displacement amplification for ultrasensitive detection of human pluripotent stem cells by Wei Wu; Yiping Mao; Shiming Zhao; Xuewen Lu; Xingguo Liang; Lingwen Zeng (124-130).
Display OmittedHuman pluripotent stem cells (hPSCs), such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide a powerful model system for studies of cellular identity and early mammalian development, which hold great promise for regenerative medicine. It is necessary to develop a convenient method to discriminate hPSCs from other cells in clinics and basic research. Herein, a simple and reliable biosensor for stem cell detection was established. In this biosensor system, stage-specific embryonic antigen-3 (SSEA-3) and stage-specific embryonic antigen-4 (SSEA-4) were used to mark human pluripotent stem cells (hPSCs). Antibody specific for SSEA-3 was coated onto magnetic beads for hPSCs enrichment, and antibody specific for SSEA-4 was conjugated with carboxyl-modified tDNA sequence which was used as template for strand displacement amplification (SDA). The amplified single strand DNA (ssDNA) was detected with a lateral flow biosensor (LFB). This biosensor is capable of detecting a minimum of 19 human embryonic stem cells by a strip reader and 100 human embryonic stem cells by the naked eye within 80 min. This approach has also shown excellent specificity to distinguish hPSCs from other types of cells, showing that it is promising for specific and handy detection of human pluripotent stem cells.
Keywords: Lateral flow biosensor; Human pluripotent stem cells; Strand displacement amplification;

Display OmittedIt was found out that semiconductor CdS nanoparticles (NPs) are able to catalyze photooxidation of the well known chromogenic enzymatic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by oxygen. The photocatalytical oxidation of TMB does not require hydrogen peroxide and its rate is directly proportional to the quantity of CdS NPs produced in situ through the interaction of Cd2+ and S2− ions in an aqueous medium. This phenomenon was applied to development of colorimetric sensitive assays for glucose oxidase and glutathione reductase based on enzymatic generation of CdS NPs acting as light-powered catalysts. Sensitivity of the developed chromogenic assays was of the same order of magnitude or even better than that of relevant fluorogenic assays. The present approach opens the possibility for the design of simple and sensitive colorimetric assays for a number of enzymes using inexpensive and available TMB as a universal chromogenic compound.
Keywords: Biosensing; Quantum dots; Glucose; Enzyme catalysis;

Display OmittedA fast, simple, and sensitive flow injection analysis method was developed for the measurement of semicarbazide-sensitive amine oxidase (SSAO) activity in human serum. Benzaldehyde, generated by the action of SSAO after incubation of serum with benzylamine, was derivatized with a novel aromatic aldehyde-specific reagent (1,2-diaminoanthraquinone) and the fluorescent product was measured by fluorescence detection at excitation and emission wavelengths of 390 and 570 nm, respectively. Serum SSAO activity was defined as benzaldehyde (nmol) formed per milliliter serum per hour. The method was linear over SSAO activity of 0.2–150.0 nmol mL−1  h−1 with a detection limit of 0.06 nmol mL−1  h−1. The %RSD of intra-day and inter-day precision did not exceed 9.4% and the accuracy ranged from −6.5 to −0.6%. The method was applied for the determination of the serum SSAO activity in healthy controls (C, n  = 24) and diabetes mellitus patients (DM, n  = 18). It was demonstrated that the activity (mean ± SE) of SSAO in diabetics sera was significantly higher than that in healthy subjects’ ones (DM; 73.3 ± 1.8 nmol mL−1  h−1 vs C; 58.9 ± 2.2 nmol mL−1  h−1, P<  0.01).
Keywords: Semicarbazide-sensitive amine oxidase activity; Benzaldehyde; 1,2-Diaminoanthraquinone; Flow injection analysis; Fluorescence detection;

Display OmittedA sensitive electrochemiluminescence (ECL) strategy for evaluating the epidermal growth factor receptor (EGFR) expression level on cell surfaces was designed by integrating the specific recognition of EGFR expressed on MCF-7 cell surfaces with an epidermal growth factor (EGF)-funtionalized CdS quantum dots (CdSQDs)-capped magnetic bead (MB) probe. The high sensitivity of ECL probe of EGF-funtionalized CdSQD-capped-MB was used for competitive recognition with EGFR expressed on cell surfaces with recombinant EGFR protein. The changes of ECL intensity depended on both the cell number and the expression level of EGFR receptor on cell surfaces. A wide linear response to cells ranging from 80 to 4 × 106  cells mL−1 with a detection limit of 40 cells mL−1 was obtained. The EGF-cytosensor was used to evaluate EGFR expression levels on MCF-7 cells, and the average number of EGFR receptor on single MCF-7 cells was 1.35 × 105 with the relative standard deviation of 4.3%. This strategy was further used for in-situ and real-time evaluating EGFR receptor expressed on cell surfaces in response to drugs stimulation at different concentration and incubation time. The proposed method provided potential applications in the detection of receptors on cancer cells and anticancer drugs screening.
Keywords: Electrochemiluminescence; Epidermal growth factor receptor; EGF-cytosensor;